In alkaline storage batteries, the electrodes commonly used are electrodes sintered at high temperature. In some applications, and for reasons of manufacturing cost, cadmium electrodes have appeared which comprise a metal support or current collector onto which an active paste is made to adhere, said active paste containing the active material per se and a binder, e.g., polytetrafluoroethylene. The function of the binder is to enable the active material to be handled in an industrial context without losing any of the active material; in addition, the binder must be entirely stable in the electrolyte used.
American Pat. No. 4,476,205 described dispersing in water a mixture of cadmium oxide together with a binder of the copolymer of carboxylated styrene-butadiene type, with the concentration of the copolymer lying in the range 3.8% to 5% of the mixture when in the dry state. The mixture is dried in order to obtain partial cross-linking of the binder; the resulting product is crushed and metal cadmium powder is incorporated therein. The electrode per se is constituted by calendering the powder mixture onto a grid or a support of expanded metal.
In order to obtain adequate mechanical performance, and to increase the cohesion of the powder which has suffered from partial cross-linking of the binder, it is necessary to apply a very high pressure to the powder mixture. This gives rise to serious drawbacks since the porosity of the active mass is low (at about 15%) and highly non-uniform, thereby hindering electrochemical formation and cadmium reactivity, generally leading to poor operation.
Preferred implementations of the present invention provide a method in which the active paste does contain a binder, but which nevertheless provides a cadmium electrode of good quality both mechanically and electrochemically.